The present invention relates to a rubber composition suitable for use in the preparation of treads of tires for passenger cars and light trucks. More particularly, the present invention relates to a rubber composition having both an excellent abrasion resistance and a low heat build-up and simultaneously a high impact resilience.
Carbon blacks for reinforcement of rubbers are classified into many different types by the properties possessed thereby. The properties of carbon blacks are a major factor which determines various characteristics of rubber compositions when the carbon blacks are compounded with a rubber to form a rubber composition. Therefore, generally, in the compounding of a carbon black with a rubber, a carbon black which can impart the properties suitable for use to the rubber component has been chosen.
For example, for these several years, intensive development efforts for low fuel consumption tires have been made in accordance with the social demand for saving resources and energy.
A low heat build-up rubber composition having a high impact resilience, in which a carbon black of a grade with a relatively large particle size is compounded with a rubber component in a relatively small amount, is useful for the preparation of low fuel consumption tires. Although compounding of a carbon black having a large particle size and a small specific surface area with a rubber component is effective in reducing the fuel consumption of tires, it makes it difficult to avoid the lowering of traction on braking on wet road surfaces and abrasion resistance.
If it is possible to impart a high abrasion resistance and a high impact resilience, together with a low heat build-up, to a rubber component by the use of a carbon black having a small particle size and a large specific surface area, which is known to effectively improve the abrasion resistance, the obtained rubber composition would be ideal as a rubber composition for use in tire treads.
Some proposals have been made on a carbon black capable of simultaneously imparting to a rubber composition a high abrasion resistance and a low heat build-up which are contradictory to each other. For example, the following proposals (a) to (f) can be mentioned.
(a) a carbon black having a nitrogen adsorption specific surface area (N.sub.2 SA) of 60 m.sup.2 /g or more, a dibutyl phthalate adsorption number of compressed sample (24M4DBP) of 112 ml/100 g or more, and each of an aggregate Stokes mode diameter and an aggregate Stokes mode distribution maintained above a specific value, which can simultaneously impart a high reinforcing performance and a high impact resilience to a compounded rubber (Japanese patent application Kokai publication No. 64-53978);
(b) a rubber composition having both a high abrasion resistance and a high impact resilience and containing a carbon black which has a N.sub.2 SA of 60 m.sup.2 /g or more, a DBP of 108 ml/100 g or more, a true specific gravity per predetermined specific surface area set within a specific range markedly lower than that of the conventional carbon blacks, and a tinting strength (Tint) and a distribution width per aggregate mode distribution each maintained above a specific value (Japanese patent application Kokai publication No. 59-140241);
(c) a carbon black having a N.sub.2 SA of from 65 to 84 m.sup.2 /g and a ratio of N.sub.2 SA to iodine adsorption number (IA) of from 1.10 to 1.35, wherein the value of a formula including as variables 24M4DBP, blackness, iodine adsorption number and aggregate mode diameter is set to be above a specific value and which can simultaneously impart a high abrasion resistance and a high impact resilience to a compounded rubber (Japanese patent application Kokai publication No. 62-58792);
(d) a carbon black having a N.sub.2 SA of from 75 to 105 m.sup.2 /g, a 24M4DBP of 110 ml/100 g or more, a true specific gravity per predetermined specific surface area set within a specific range markedly lower than that of the conventional carbon blacks, and each of an intraaggregate pore diameter and a distribution width per aggregate mode diameter set above a specific value, which can simultaneously impart a high abrasion resistance and a high impact resilience to a compounded rubber (Japanese patent application Kokai publication No. 64-201367);
(e) a carbon black for use in tire tread rubbers which has a N.sub.2 SA of from 85 to 95 m.sup.2 /g, a 24M4DBP of from 100 to 104 ml/100 g, a Tint of from 95 to 100% and a mode distribution of the aggregate Stokes diameter (.DELTA.D.sub.50) of 180 .mu.m or more, and which can attain a high abrasion resistance and a high impact resilience (U.S. Pat. No. 4,360,627); and
(f) a carbon black for use in tire tread rubbers for energy saving, having a N.sub.2 SA of from 75 to 105 m.sup.2 /g, satisfying the relationships N.sub.2 SA-IA.gtoreq.15, N.sub.2 SA-CTAB (cetyltrimethylammonium bromide) surface area .ltoreq.5, 24M4DBP.ltoreq.110, Tint=90 to 110 and .DELTA.Tint.ltoreq.-3, and capable of imparting a low rolling resistance and a high wet traction performance to a rubber composition (U.S. Pat. No. 4,548,980).
Despite the above proposals, the requirement for low fuel consumption tires is escalating and the demand for the development of a low heat build-up rubber composition having a high impact resilience while maintaining an excellent abrasion resistance is still strong in the art.